The trajectory of a sports projectile in free flight is characterized by steadily changing coordinates of position and velocity. Certain more limited characteristics of the full trajectory may be of special interest, however—notably, the component of the initial release speed in the intended direction of flight. This is what is typically meant when referring to the “speed” of a pitch in baseball, or of a serve in tennis, or of a slapshot in hockey. There is a need, therefore, for accurate and practical devices to measure such speeds.
In recent years, such measurements have been made somewhat more practicable by the development of the radar gun, wherein the rate of change of the projectile's distance from the device (its “range rate”) is taken from the Doppler shift of a reflected microwave signal. The release speed of the projectile may then be equated with the greatest range-rate measurement seen, as the speed of the sports projectiles of interest generally decrease monotonically after release.
Obtaining an accurate speed in this manner, however, is subject to difficulties and limitations. For instance, range-rate accurately reflects projectile speed only when the projectile is traveling straight at the measuring device. It may not be practical to meet this constraint if the intended path is not known in advance, or if the suitable locations for measurement are inaccessible, required for other uses, or out of the device's effective range. When the angle “theta” between the measuring line to the projectile and the projectile's line of travel is not zero, the measured speed will be diminished by a factor equal to the cosine of theta. The resulting error is sometimes known as the “cosine effect”.
In addition, a range-rate measurement will be reflective of release speed only if it is taken at the moment just after release. A baseball pitch, for instance, may lose ten miles per hour on its way to the plate, due to air drag—the exact amount depending on initial speed and pitching distance, among other things. Late detection of the pitch also complicates the effect of cosine error. Since the measuring device is unlikely to be perfectly located, the relevant theta is likely to increase with time, and the degree of cosine error will be greater, the later the device first “picks up” the pitch. Theta will also change with time due to a path curvature that is usually dominated by gravitational arc.
Thus a conventional radar gun may be difficult to use properly. Furthermore, a conventional radar gun of sufficient quality and sensitivity to give reliable and accurate readings when used properly can be an expensive device.
Although briefly discussed above in terms of the baseball pitch, analogous problems apply to measuring the speeds of other sports projectiles.
Therefore, there is a continuing need for an improved method for measuring the true speed of a sports projectile.
More particularly, there is a need for such a method in application to an inexpensive and convenient pitching trainer device. There exist passive targets for pitching practice, but these do not provide all the performance feedback desired. To monitor pitch velocity, an additional person must typically be dedicated to operating a separate speed-measuring device, such as a radar gun, and calling out the results. Pitch capture nets may provide some indication of ball/strike performance, but require hand tallying of all balls retrieved from both inside and outside the nets. Also, the mechanical design of existing targets can be deficient, with pitches of even moderate speed able to cause significant damage.
Therefore, there is need for a pitching trainer device that presents the speed of each pitch to the user without the user needing to leave his pitching position, and without tying up another individual in holding a radar gun or reporting speeds. There is also a need for such a device, without significant additional complexity, to be able to report and tally ball/strike performance. There is also need for such a device with improved robustness of design.